Second harmonic nonlinear amplifier



Sept. 28, 1948. o. w. LIVINGSTON SECOND HARMONIC NONLINEAR AMPLIFIER Filed May '7, 1948 Figi.

by /D His AcizovreyA Patented Sept. 28, 1948 SECOND HABMONIO NONLINEAB AMIPLIFIEB l Orrin W. Livingston. Scotia, N. Y., assigner to General Electric Company, a corporation of New York Application May 7, 194B, Serial No. 25.503

'i Claims. (Cl. 172-281) proved second harmonic non-linear amplifier re- Y quiring no rectiiiers or non-linear impedances other than the saturable reactor windings.

Another object of my invention is to pro 'ide an improved second harmonic non-linear .im--

pllder adapted to supply two output voltages 180 out of phase with each other for operation into push-pull electronic circuits.

A further object of my invention is to provide an improved amplifier of the type described in which voltages induced in the input signal windings are cancelled out so that these induced voltages cause no undesirable circulating currents in the` circuits connected to the amplifier input; nor does the output circuit short circuit the second harmonic voltages produced by the amplifier.

The features of my invention which are believed to be novel and patentable are pointed out in the claims appended hereto. For a better understanding of my invention. reference is made in the following kdescription to the acompanying drawing in which Fig. 1 is a schematic diagram of a basic element of my improved amplifier; Fig. 2 is a schematic diagram of two such elements combined to provide a push-pull output; Fig. 3 is a schematic diagram of a preferred embpdiment of my invention combining av push pull output and cancellation of induced voltages in the input windings; and Fig. 4 is a graphic representation which will be used in explaining the operation of my invention. Like reference characters refer to similar parts throughout the drawing.

Referring now to Fig. l, a saturable magnetic core I is preferably constructed in two sections as shown. but may be a single three-legged core or may b'e one of numerous other core designs known in the art. Wound upon the core is a reactor winding comprising two similar sections 2 and i which are connected together in series. The entire winding is then connected directly to asource of alternating current I which may be two terminals, as shown, for connection to a 60 cycle commercial line or other convenient alternating current supply. Also wound about core i is a signal winding 5 through which may be passed a direct current signal. It should be noted that the magnetic flux produced by direct current in the signal winding flows in opposite directions through sections 2 and I of the reactor winding. Thus. if such iiux flows clockwise through the signal winding and section 2 of the reactor winding, it must flow counterclockwise through the signal winding and section 3 of the reactor winding.

Connected in parallel with the reactor winding is an impedance l, preferably a resistor as shown. Output terminals 1 and I are respectively connected lto a point in the circuit between the two sections in the reactor winding and to a tap substantially at the center of impedance element l. Preferably this tap is adjustable. The reactor winding and impedance element l in effect form a bridge circuit, with the alternating current source connected across two opposite corners of the bridge, and with the terminals 1 and l connected to the other two corners of the bridge. The tap of impedance 5 should be adjusted so that the bridge is balanced and no fundamental frequency alternating component of voltage appears between terminals 1 and l. An adjustable resistor l and a capacitor le in series may be connected between the tap and either end of impedance element 5 to balance out any quadrature component of fundamental frequency voltage which might appear between terminals 1 and I due to slight dissimllarlties between corresponding parts in opposite .sides nf the circuit, which would cause the circuit to be somewhat unsymmetrical.

Referring now to Fig. 4, curve 2t is a graphical representation of a. typical magnetic hysteresis curvein which magnetic flux density B is plotted as a function of the magnetizing force H. Curve 25 represents an alternating magnetizing force provided by current flowing in the reactor winding of a second harmonic non-linear amplifier. In curve25, the abscissa is H, as for curve 24, and the ordinate is time. The vertical axis of curve 25 is shown displaced a small amount from the vertical axis of curve 24. This displacement represents a unidirectional magnetizing force provided by direct current flowing in the amplifier signal winding. The resulting magnetic flux density in the core is represented by curve 26, constructed so that corresponding points of curves 25 and 26 have a. common projection upon curve 2l. In curve 25, -'the ordinate is B, as for curve 2l, and the abscissa is time. It should be noted that curve 26 is not sinusoidal in shape: therefore, it must contain harmonic components. To illustrate, consider a second alternating magnetic force represented by curve 21 180 out of phase with curve 25. This produces a magnetic ux density representedby curve 2l. Adding curves 25 and 28 the fundamental frequency components the axis of curves and 21, the amplitude of curve 29 is substantially proportional to such displacement; and that reversing the direction of such displacement reverses the phase of curve 28.

Referring again to Fig. 1, direct current flowing through signal winding 5 provides a unidirectional magnetizing force in core I, and the alternating current flowing through sections 2 and 8 of the reactor winding provides alternating magnetizing forces. These magnetizing forces produce flux densities in core I which have unsymmetrical wave forms as hereinbefore described; and since flux produced by currentin winding 5 flows in opposite directions through sections 2 and 3 of the reactor winding. the total magnetizing forces near these sections are displaced in opposite directions respectively from the vertical axis of the B-H curve, so that the respective flux densities in the top and bottom portions of core I reach their maximum during opposite half cycles of the applied alternating current. This causes asecond harmonic component of potential at output terminal 1, and since there is no second harmonic component in the potentiaiof terminal 8 there is a second harmonic output voltage between terminals 1 and 8 which is proportional to the direct current flowing through winding 5 times the number of turns on this winding; and the phase of this output voltage is determined by the direction of current flow through winding 5. By providing a large number of turns on winding 5, very feeble direct currents can be made to produce second harmonic output voltages of substantial magnitude.

A disadvantage of the circuit just described is that second harmonic voltage is induced in winding 5 by the second harmonic flux in the core. Thus, when this circuit is used with a low impedance input circuit a filter or a large choke should be connected in series with the input to reduce the now of circulating currents and to prevent decreasing the value of the 2nd harmonic output voltage by the short circuiting or loading effect of the signal circuit. This disadvantage is overcome in the circuit of Fig. 3, hereinafter described.

Referring now to Fig. 2, two basic elements.

`as hereinbefore described, are combined to provide two output voltages 180 outl of phase with each other. Like numbered parts are the same as in Fig. 1 and throughout all figures of the drawing. saturable magnetic core II is similar to core I, and has a reactor winding comprising two sections I2 and I3 similar to the reactor windings comprising sections v2 and 3 wound upon core I. Signal winding I4, wound upon core II, is connected in series with signal winding 5 wound upon core I. Output terminal I5 is connected to an output circuit .between the two reactor sections I2 and I3. It should be noted that the reactor winding on core II is Wound in the same direction as the reactor wind- -ing on core I, but that signal winding I4 is wound in a direction opposite to that of signal Winding 5, This reversal of the signal winding relative to the reactor winding results in an inversion of the second harmonic component Ofpotential at terminal t8, so that the second harmonic voltage between terminals Il and 8 is 180 out of phase with the second. harmonic component of voltage between terminals 1 and 8. Thus, this circuit may be utilized to obtain an output voltage of double amplitude by connecting an output circuit between terminals 1 and I5, or all three output terminals may be used for connection to a push-pull electronic circuit. The circuit of Fig. 2, however, has the same disadvantage as the circuit of Fig. 1, that second harmonic voltage lis induced in the signal windings which tends to cause circulating currents in the input circuits.

In Fig. 3 I have shown a preferred embodiment of my invention which combines the features of push-pull output with means for cancelling the voltages induced in the signal windings, This circuit utilizes another method of -obtaining second harmonic voltages 180 out of phase with eachother: a 90 phase shift of the fundamental frequency components in one of the reactors which results in a 180 phase shift of the second harmonic components. In the circuit of Fig. 3, I accomplish this phase shift by connecting source 4 to a phase shifting network comprising resistors I8 and I1 and capacitors I8 and I9,` This phase shifting network provides a current through the primary of transformer 20 which is 90 out of phase with alternating current source 4. A secondary of transformer 20 is connected to the reactor Winding upon saturable core II so that the fundamental frequency components of flux in core II are out of phase with the fundamental frequency components of flux in core I. Thus, the second harmonic components in the two circuits are out of phase, so that voltages of opposite phase are again obtained between terminals 1 and 8 and I5 and 8. However, in this embodiment, the second harmonic components are also 180 out of phase in the two signal windings 5 and I4, so that the voltages induced in these two windings cancel out and there is therefore no net induced voltage in the signal winding to cause circulating currents.

In this embodiment of my invention, an impedance-element 2I is connected in parallel with the reactor winding upon core II. This impedance element 2i is similar to impedance element 8, and the taps of the two impedance elements are connected together. If both taps are adjustable, fundamental frequency components of voltage can be balanced out between terminals 1 and 8 and between terminals I5 and 8 independently, and thus the most nearly perfect elimination of these components can be obtained. Resistor 22 and capacitor 23, similar to resistor 9 and capacitor I0, may also be provided to aid in balancing out quadrature components of fundamental frequency voltage.

In accordance with the provisions of the patent statutes, I have described the principle of my invention together with apparatus which I now consider to represent the best embodiment thereof; but I wish it to be understood that the apparatus described is illustrative only and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. In a second harmonic non-linear amplifier, the combination of alternating current supply connections, a saturable magnetic core, a reactor winding and at least one signal winding upon said core, said reactor winding comprising two series-connected similar sections and being connected directly to the alternating current supply connections, said signal winding .being so disposed relative tothe reactor winding that magnetic flux produced by direct current in the signal winding iiows in opposite directions through respective sections of the reactor winding, an impedance element connected in parallel with said reactor winding, and output connections respectively connected to a point in the circuit between the two sections of the reactor winding and to a tap substantially at the center of said impedance element; so that substantially no fundamental frequency component of voltage appears between said output connections.

2. In a second harmonic non-linear amplier, the combination of alternating current supply connections, a saturable magnetic core, a reactor winding and at least one signal winding upon said core, said reactor winding comprising two series-connected similar sections and being connected directly to the alternating current supply connections, said signal winding being so disposed relative to the reactor winding that magnetic flux produced by direct current in the signal winding iiows in opposite directions through respective sections of the reactor winding, a first resistor connector in parallel with said reactor winding and having an adjustable tap, a variable resistor and al capacitor in series connected between said tap and one end of said rst resistor, and output connections respectively connected to a point in the circuit between the two sections of the reactor winding and to said tap,

so that said tap and said variable resistor can be adjusted to substantially eliminate fundamental frequency components of voltage between said output connections.

3. In a second harmonic non-linear amplifier, the combination of two saturable magnetic cores each having thereon a reactor vwinding comprising two series-connected similar sections, means to provide alternating currents through said ,reactor windings, signal windings so disposed relative to each reactor winding that magnetic flux produced in each core by direct current in the signal windings iiows in opposite directions through the two sections of each reactor winding, and output connections respectively connected to points in the circuit between the two sections of each reactor winding, the

relative dispositions of said windings and the phase relations4 of currents therethrough being such that the respective second-harmonic components of potential of said output connections are 180 out of phase with each other to provide a maximum second-harmonic component of voltage between said connections.

4. In a second harmonic non-linear amplifier,

the combination-of two saturable magnetic cores each having thereon a reactor winding comprising two series-connected similar sections, means to provide alternating currents through said reactor windings, signal windings so disposed relative to each reactor winding that magnetic nux produced in each core vby direct current in the vsignal windings. flows in opposite directions through the two sections of each reactor win-ding, an impedance element connected in parallel with said source of alternating current, first and second output connections respectively connected to mints in the circuit between the two sections 6 of each reactor winding, and a third output connectionv connected to a tap substantially at the center of said impedance element, the relative dispositions of said windings and the phase relations of currents therethrough being such that the respective second harmonic components of voltage between the rst and third output connections and between the second and third output connections are 180 out of phase with each other.

5. In a second harmonic non-linear amplifier, the combination of two saturable magnetic cores each having thereon a reactor winding comprising two series-connected similar sections, means to provide alternating currents through said reactor windings, the respective currents through said windings having a phase difference of signal windings so disposed relative to each reactor winding that magnetic iiux produced in each corel by direct current in the signal windings ows in opposite directions through the two sections of each reactor winding, and output connections respectively connected to points in the circuit between the two sections of each reactor winding.

6. In a second harmonic non-linear amplifier, the combination of two saturable magnetic cores each having thereon a reactor winding comprising two series-connected similar sections, means to provide alternating currents through said reactor windings, the respective currents through said windings having a phase difference of 90, signal windings so disposed relative to each reactor winding that magnetic flux produced in each core by direct current in the signal windings flows in opposite directions through the two sections of each reactor winding, two impedance elements respectively connected in parallel with said reactor windings, rst and second output connections respectively connected to points in the circuit between the two sections of each reactor winding, and a third output connection connected to two taps respectively located substantially at the centers of said two impedance elements.

7 A second harmonic non-linear amplifier comprising rst and second saturable magnetic cores, rst and second reactor windings respectively wound upon said cores, each such reactor winding comprising two series-connected similar sections, a source of alternating current, connections from said source to said first reactor winding for providing an alternating current therethrough, connections including a phase-shifting network and a transformer from said source to said second reactor winding for providing a current therethrough having a phase difference of 90 from the current through the lirst reactor winding, signal windings so disposed relative to each reactor winding that magnetic -flux produced in each core by direct current in the signal windings flows in opposite directions through the two sections of' each reactor winding, two impedance elements respectively connected in parallel with said reactor windings, rst and second output connections respectively connected to points in the circuit between the two sections of each reactor winding, and a third output connection connected tostwo taps respectively located substantially at the centers of said two impedance elements.

ORRIN W. LIVINGSTON.

No references cited. 

